O'Hara was 41 years old when the Civil War began.
was admitted to the bar in 1842. He decided to forgo law and went to journalism in 1845, just before being appointed for a position in the United States Treasury Department in 1845.
As the Mexican-American War was beginning, O'Hara signed up for the U.S. Army on June 26, 1846. He served under General Gideon J. Pillow as they advanced upon Mexico City.
O’Hara wrote the poem, “Bivouac of the Dead” as a remembrance of the many casualties suffered by the Second Kentucky Regiment of Foot Volunteers who fought at the Battle of Buena Vista. The verse was produced for the dedication ceremony for a monument erected to the men. The battle of February 22-23, 1847, saw 4,759 Americans under the command of General Zachary Taylor repulse an estimated force of 18,000 Mexicans led by President Antonio Lopez de Santa Anna. More Americans fell at Buena Vista—267 killed and 456 wounded—than any other battle in the war.
O'Hara was honorably discharged on October 15, 1848. After the war ended in 1848, O'Hara returned to Washington, D.C. to continue his law practices until 1851.
Lopez, O'Hara commanded a regiment, with the rank of colonel, in the hopes of removing Spanish rule from Cuba. In the battle of Cardenas on May 18, 1850, he suffered a severe injury. After Lopez failed and died in his Cuba position in 1851, O'Hara returned to Kentucky, after fellow Kentuckians serving in Cuba took him with them as they escaped, returning to the United States.
|Grave of Theodore O'Hara|
The muffled drum's sad roll has beat
The soldier's last tattoo;
No more on Life's parade shall meet
That brave and fallen few.
On fame's eternal camping ground
Their silent tents to spread,
And glory guards, with solemn round
The bivouac of the dead.
Because he served for the Confederacy, O'Hara often goes uncredited when the quatrain is used in a non-Confederate cemetery setting. Although stanzas from Theodore O’Hara’s poem, “Bivouac of the Dead,” are inscribed on iron tablets found throughout this country’s national cemeteries, there is little public recognition of this poet-soldier. Quartermaster General Montgomery C. Meigs directed that lines from “Bivouac” grace the entrance to Arlington National Cemetery.